.xcdatamodel: cdtool cannot compile

One solution posted on the Apple developer forums is renaming a file within the iOS Simulator.

cd /Applications/Xcode-beta.app
cd Contents/Developer/Platforms/iPhoneSimulator.platform  
cd Developer/SDKs/iPhoneSimulator.sdk/usr/lib  
sudo mv dyld_sim dyld_sim.orig

Here's the original link.

This solution unfortunately did not work for me. However, I had recently changed some tables around in core data. I found the culprit by looking at all of my relationships and their inverses. One of the inverses had a dead reference. Switched it to "no inverse" did a clean and was up and running again. Hope this helps someone else.